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Direct measurement of oxygen partial pressure in a flying bumblebee

Yutaka Komai^*

ERATO, Kawachi Millibioflight Project, Park Building, 4-7-6 Komaba, Meguro, Tokyo, Japan

View larger version (25K): [in a new window]   Fig. 1. Diagram of a tethered bumblebee showing the region of cuticle that was removed for electrode insertion. In this dorsal view, the tether extends to the left. In the enlarged area, the electrode is shown inserted along path 1 (see Fig.2)

View larger version (24K): [in a new window]   Fig. 2. Longitudinal section of the bumblebee thorax to show the two directions in which the electrodes were inserted (arrows). The hatched boxes were removed; the cuticle and muscle were removed for path 1, and the cuticle and air sac were removed for path 2. DLM, dorsal longitudinal muscle.

View larger version (28K): [in a new window]   Fig. 3. Variation in flight muscle PO2 in a resting bumblebee. (A) Representative pattern; PO2 showed large-amplitude fluctuations. In this recording, the bee began to move its legs rapidly at 18:03min, disrupting the regular pattern. Horizontal bars indicate periods of abdominal pumping. Asterisks indicate other abdominal movements. (B) Small-amplitude and short-interval PO2 fluctuations observed under some conditions. This pattern was seen in four of the six animals when the room temperature was above 30°C and in one of the six animals when the room temperature was below 30°C. (C) Pattern recorded in a bee anaesthetised using chloroform vapour. The bee began ventilating at approximately 5min. Thin and thick horizontal bars indicate periods of abdominal pumping and a pattern peculiar to anaesthesia, respectively. Flattened PO2 peaks following abdominal ventilation were observed only during recovery from anaesthesia. (D) Effects of cooling the bee using an ice pack. (E) Recording from the same animal shown in D, but during rewarming to room temperature. See Table1 for experimental conditions.

View larger version (35K): [in a new window]   Fig. 4. Effects of non-ventilatory period on flight muscle PO2 fluctuation amplitude (filled symbols) and minimum value (open symbols) for three different experiments (squares, run 1; circles, run 4; diamonds, run 5; experimental condition are listed in Table1). Correlation coefficients (r) between amplitude and period are 0.373, 0.824 and 0.356 (all P<0.01) and between minimum PO2 and period are -0.517 (P<0.01), -0.061 (not significant) and -0.863 (P<0.01) for run 1 (N=49), run 4 (N=80) and run 5 (N=33), respectively.

View larger version (18K): [in a new window]   Fig. 5. Vertical PO2 profile in the dorsal longitudinal muscle of two tetrodotoxin-paralyzed bees. Visible movements were not observed during measurements. PO2 values were averaged over 15s. Error bars show ± S.D. The asterisk identifies one example of the distance between two maxima.

View larger version (18K): [in a new window]   Fig. 6. Histogram of the distance between PO2 peaks (maximum) and troughs (minimum) found in the vertical PO2 profiles of the dorsal longitudinal muscle. See Fig.5 for a definition of the distance measured. Results are from 25 animals.

View larger version (18K): [in a new window]   Fig. 7. Variation in muscle PO2 during tethered flight. Bold lines correspond to periods of wing movement similar to flight; broken lines correspond to other movements of the legs or opening and closing of the wings. Traces are from a single bee with the oxygen electrode inserted into the thorax at different depths: (A) 500µm; (B) 1000µm; (C) 1500µm; (D) 2000µm. See Table1 for experimental conditions.

View larger version (24K): [in a new window]   Fig. 8. Rate of change in muscle PO2 (dPO2/dt) relative to the onset of abdominal pumping or flight. Circles indicate run 1 (N=7) and squares indicate run 3 (N=7). Values are means ± S.D. Lines without symbols are for run 8 (N=7). The abscissa is relative time from the onset of abdominal pumping for runs 1 and 3, and from the onset of flight for run 8. Experimental conditions are listed in Table1.